14 research outputs found
Multidecadal persistence of organic matter in soils: multiscale investigations down to the submicron scale
Minerals, particularly clay-sized minerals, protect soil
organic matter (SOM) from decomposition by microorganisms. Here we report
the characterization of SOM and the associated minerals over decades of
biodegradation, in a French long-term bare fallow (LTBF) experiment started
in 1928. The amounts of carbon (C) and nitrogen (N) in the study area declined over time for
six fractions (sand, coarse silt, fine silt, coarse clays, intermediate
clays, and fine clays). The C:N ratios of SOM associated with silt fractions
remained constant, whereas the ratios significantly decreased in clays, reaching
very low values in intermediate and fine clays (C:N <â5) after
8Â decades of LTBF conditions. X-ray absorption spectroscopy revealed the following: (i)Â bulk-scale
SOM chemical speciation remained almost constant; (ii)Â submicron
particulate OM was present in coarse clays, even after 79Â years of LTBF
conditions; and (iii)Â illite particles became progressively SOM-free with time, whereas mixed-layer
illite/smectite and smectites were always associated with OM
throughout the bare fallow treatment. In summary, these results suggest that
clay-sized minerals preferentially protect N-rich SOM and that smectites and
mixed-layer illite/smectite seem to protect associated OM more effectively
than pure illites.</p
Early precipitated micropyrite in microbialites: A time capsule of microbial sulfur cycling
Microbialites are organosedimentary rocks that have occurred throughout the Earthâs
history. The relationships between diverse microbial metabolic activities and isotopic
signatures in biominerals forming within these microbialites are key to understanding
modern biogeochemical cycles, but also for accurate interpretation of the geologic
record. Here, we performed detailed mineralogical investigations coupled with
NanoSIMS (Nanoscale Secondary Ion Mass Spectrometry) analyses of pyrite S
isotopes in mineralising microbial mats from two different environments, a hypersaline
lagoon (Cayo Coco, Cuba) and a volcanic alkaline crater lake (Atexcac, Mexico).
Both microbialite samples contain two distinct pyrite morphologies: framboids and
euhedral micropyrites, which display distinct ranges of ÎŽ34S values1. Considering
the sulfate-sulfur isotopic compositions associated with both environments, micropyrites display a remarkably narrow range
of Îpyr (i.e. Îpyr ⥠Ύ34SSO4 â ÎŽ34Spyr) between 56 and 62â°. These measured Îpyr values agree with sulfate-sulfide equilibrium
fractionation, as observed in natural settings characterised by low microbial sulfate reduction respiration rates. Moreover, the
distribution of S isotope compositions recorded in the studied micropyrites suggests that sulfide oxidation also occurred at
the microbialite scale. These results highlight the potential of micropyrites to capture signatures of microbial sulfur cycling
and show that S isotope composition in pyrites record primarily the local micro-environments induced by the microbialite
A new fast multi-domain BEM to model seismic wave propagation and amplification in 3D geological structures
International audienceThe analysis of seismic wave propagation and amplification in complex geological structures raises the need for efficient and accurate numerical methods. The solution of the elastodynamic equations using traditional boundary element methods (BEMs) is greatly hindered by the fully-populated nature of the matrix equations arising from the discretization. In a previous study limited to homogeneous media, the present authors have established that the Fast Multipole (FM) method reduces the complexity of a 3-D elastodynamic BEM to per GMRES iteration and demonstrated its effectiveness on 3-D canyon configurations. In this article, the frequency-domain FM-BEM methodology is extented to 3-D elastic wave propagation in piecewise-homogeneous domains in the form of a FM-accelerated multi-region BE-BE coupling approach. This new method considerably enhances the capability of the BEM for studying the propagation of seismic waves in 3-D alluvial basins of arbitrary geometry embedded in semi-infinite media. Several fully 3-D examples (oblique SV-waves) representative of such configurations validate and demonstrate the capabilities of the multi-domain fast multipole approach. They include comparisons with available (low-frequency) results for various types of incident wavefields, and time-domain results obtained by means of Fourier synthesis
Catalogue de la bibliothÚque de la ville d'Annonay. Suppl. 1 / mis en ordre par le Dr Alléon,...
Appartient Ă lâensemble documentaire : RhoneAlp
Catalogue de la bibliothÚque de la ville d'Annonay. 1 / mis en ordre par le Dr Alléon,...
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Travail. (Signé : Le maire provisoire, Alléon. 27 mars 1848.)
Appartient Ă lâensemble documentaire : RhoneAlp1Avec mode text
Corrigendum to "Early precipitated micropyrite in microbialites: a capsule of microbial sulfur cycling" by Marin-Carbonne et al., 2022.
International audienc